A heart works as a pump that sends a blood to the whole body by way of an aorta. For example, a cardiac valve (aortic valve), that is formed at the exit where the blood flows out from a left ventricle to the aorta, is composed of cup-shaped three valve cusps of a thin membrane. In a state that a fluid pressure of a blood flow is low, inner membranes of the valve cusps are joined to each other to close the cardiac valve, thereby blocking the blood flow. Whereas, when the fluid pressure of the blood flow is increased, the inner membranes of the valve cusps are spaced apart from each other to open the cardiac valve, thereby allowing the blood to flow from the heart into the aorta. Each of the valve cusps has commissure portions corresponding to a left end and a right end thereof, and each of the valve cusps is integrated with an inner wall of the aorta at the commissure portions.
When arteriosclerosis, etc. proceed along with aging, calcium is deposited to the valve cusps and thereby calcifying and hardening the valve cusps. This phenomenon causes a disease of an aortic valve stenosis in which the movement of the valve cusps is restricted and the valve cusps open insufficiently. As a result, the left ventricle wall becomes thicker to be enlarged. When the thickness of a wall of the cardiac muscle is excessively increased, nutrition and oxygen delivered by the blood flow supplied from the coronary arteries are insufficient. This results in a myocardial ischemia (a state of insufficient nutrition and oxygen) of the heart. Particularly, if the myocardial ischemia is caused when the oxygen demand is increased, for example, during activity, it may possibly cause symptoms such as chest pain and syncope.
As a result of an earnest study, the present inventor has established an aortic valvuloplasty, instead of a conventional valve replacement, as therapeutics for such a disease. The aortic valvuloplasty is a technique as follows. That is, among the valve cusps hardened due to deposition of calcium, valve cusps that can be used by decalcification are left as much as possible, and only valve cusps that cannot be used are excised to be repaired by replacing the excised valve cusps with another aortic valve formed of autologous biomembrane, etc. In this case, since the valve cusps are formed by an autologous pericardium to be used as a new aortic valve, there is no problem of causing rejection or blood clotting reaction (thrombus) and purchasing an expensive prosthetic valve is not required. In the aortic valvuloplasty, a new valve cusp conforming to the diameter of a patient's aorta is required to be cutout from a planar pericardium. However, there has been a problem how to determine the size of the new valve cusp conforming to the diameter of the patient's aorta.
Therefore, the inventor of the present invention developed a valve cusp forming instrument for measuring the size of a patient's valve cusp accurately and forming a valve cusp conforming to the diameter of the patient's aorta (see Patent Document 1). Patent Document 1 discloses a valve cusp forming instrument for using in the aortic valvuloplasty. The valve cusp forming instrument includes a plurality of valve cusp sizers and templates. An example of valve cusp sizer is shown in FIG. 2 of Patent Document 1. A photograph of an actual valve cusp sizer is shown in FIG. 8 of the present application. As shown in FIG. 8 and the like, the conventional valve cusp sizer has a sizer block and a grip member attached to the sizer block. The sizer block has an arcuate surface formed by cutting a column at an angle conforming to the central angle for the commissure portions of the valve cusp. The sizer block is also provided with contact probe portions for positioning both ends of the arcuate surface to the commissure portions of the valve cusp. In the valve cusp forming instrument disclosed in Patent Document 1, each of a plurality of differently-sized sizer blocks are connected to a plurality of grip members to be gripped by hands, as shown in FIG. 1 of Patent Document 1.
The aortic valvuloplasty is disclosed in Shigeyuki OZAKI “Jiko Shinmaku Wo Shiyou Shita Daidoumyakuben Keiseijutsu [Aortic valvuloplasty using autologous pericardium]” Jinko Zoki, Vol. 39 (2010), No. 3, 157-161. (see Non-Patent Literature 1 below.) Non-Patent Literature 1 discloses a valve cusp sizer including a sizer block and a grip member as described above (see FIG. 2 of Non-Patent Literature 1).